FIGS. 1(a) through 1(d) are cross-sectional views for illustrating a first separation method of a liquid crystal mother substrate in a step-by-step manner as an example of a conventional procedure for cutting a bonded glass substrate, such as a liquid crystal mother substrate, at a desired cutting position. In the following descriptions, in a bonded glass substrate formed by a pair of glass substrates, which is a liquid crystal mother substrate, one of the glass substrates is referred to as an A-side glass substrate, and the other glass substrate is referred to as a B-side glass substrate, for convenience of explanation.
(1) First, as shown in FIG. 1(a), the bonded glass substrate 1 is placed on a first scribing apparatus such that the A-side glass substrate is laid over the B-side glass substrate, and the A-side glass substrate is scribed using a glass cutter wheel 2 so as to form a scribe line Sa.
(2) Next, the bonded glass substrate 1 in which the scribe line Sa was formed in the A-side glass substrate is turned over, and transported to a second scribing apparatus. In this second scribing apparatus, the B-side glass substrate of the bonded glass substrate 1 is scribed using a glass cutter wheel 2 so as to form a scribe line Sb which is parallel to the scribe line Sa as shown in FIG. 1(b). It should be herein noted that, in the case of a liquid crystal mother substrate, a plurality of liquid crystal panels are formed from the liquid crystal mother substrate, and in each liquid crystal panel, it is necessary to form terminals at a side edge portion in one glass substrate. Thus, in many cases, the scribing position of the scribe line Sa formed in the A-side glass substrate and the scribing position of the scribe line Sb formed in the B-side glass substrate are shifted from each other along a horizontal direction as shown in FIG. 1(b).
(3) Next, the bonded glass substrate 1 where the scribe lines Sa and Sb were formed in the A-side glass substrate and the B-side glass substrate, respectively, is transported to a first breaking apparatus without being turned over, i.e., without exchanging the positions of the A-side glass substrate and the B-side glass substrate. In the first breaking apparatus, as shown in FIG. 1(c), the bonded glass substrate 1 is placed on a mat 4. A break bar 3 is pushed against the B-side glass substrate of the bonded glass substrate 1 along the scribe line Sa formed in the A-side glass substrate. As a result, a crack extends upwardly from the scribe line Sa, and accordingly, the lower A-side glass substrate is broken along the scribe line Sa.
(4) Next, the bonded glass substrate 1 in which the A-side glass substrate was broken is turned over such that the A-side glass substrate is over the B-side glass substrate, and transported to a second breaking apparatus. In the second breaking apparatus, as shown in FIG. 1(d), the bonded glass substrate 1 is placed on a mat 4. A break bar 3 is pushed against the A-side glass substrate of the bonded glass substrate 1 along the scribe line Sb formed in the B-side glass substrate. As a result, the lower B-side glass substrate is broken along the scribe line Sb.
By performing above steps (1) through (4), the bonded glass substrate 1 is separated into two at desired positions.
As illustrated in above steps (3) and (4), the break bar 3 is pushed against the upper glass substrate, whereby the lower glass substrate is broken. For example, as shown in FIG. 1(c), when the break bar 3 is pushed against the upper B-side glass substrate, the A-side glass substrate and the B-side glass substrate are bent downward at a position against which the break bar 3 is pushed, whereby force is applied to the A-side glass substrate so as to horizontally widen the crack formed along the vertical direction (vertical crack) of the scribe line Sa formed in the A-side glass substrate. As a result, the vertical crack extends upwardly so as to reach the upper surface of the A-side glass substrate, whereby the A-side glass substrate is separated. On the other hand, in the scribe line Sb formed in the upper B-side glass substrate, force in a horizontal direction from both ends of the B-side glass substrate toward the crack, which is the opposite direction to that of the force caused in the lower glass substrate, is applied so as to compress the crack (vertical crack). Therefore, the B-side glass substrate is not broken.
In the breaking steps performed at steps (3) and (4), when the vertical crack of the scribe line Sa of the lower A-side glass substrate is shallow as shown in FIG. 1(c), it is necessary to apply a relatively large pushing force in order to break the A-side glass substrate. However, when the pushing force applied by the break bar 3 is too strong, the upper B-side glass substrate may be broken simultaneously with the A-side glass substrate. In this case, in the lower A-side glass substrate, the vertical crack extends along a substantially vertical direction to break the lower A-side glass substrate, i.e., no problem is caused. However, since in the upper B-side glass substrate, the position where the force is applied by the break bar 3 is different from the position of the scribe line Sb formed in the B-side glass substrate, force is not caused in a direction such that the upper B-side glass substrate is broken. Thus, a separation face may be formed in an oblique direction. Furthermore, cracks may be formed so as to be in contact with each other so that defects (horizontal cracks) are caused at that position of contact. A bonded glass substrate having such a separation face extending along an oblique direction, or such defects, has no commercial value as a liquid crystal panel.
The applicant of the present application has proposed a separation method of a brittle substrate which can solve such problems in Japanese Laid-Open Publication No. 6-48755 entitled “Separation Method of Bonded Glass Substrate”.
FIGS. 2(a) through 2(d) are cross-sectional views which illustrate a second separation method for separating a brittle material, which is described in the above publication, in a step-by-step manner. Hereinafter, the method described in this publication is described with reference to FIGS. 2(a) through 2(d). In the following descriptions also, as referred to in FIGS. 1(a) through 1(d), in a bonded glass substrate formed by a pair of glass substrates, which is a liquid crystal mother substrate, one of the glass substrates is referred to as an A-side glass substrate, and the other glass substrate is referred to as a B-side glass substrate, for convenience of explanation.
(1) First, as shown in FIG. 2(a), the bonded glass substrate 1 is placed on a first scribing apparatus such that the A-side glass substrate is over the B-side glass substrate, and the A-side glass substrate is scribed using a glass cutter wheel 2 so as to form a scribe line Sa.
(2) Next, the bonded glass substrate 1 where the scribe line Sa was formed in the A-side glass substrate is turned over, and transported to a first breaking apparatus. In this first breaking apparatus, as shown in FIG. 2(b), the bonded glass substrate 1 is placed on a mat 4. A break bar 3 is pushed against the B-side glass substrate of the bonded glass substrate 1 along the scribe line Sa formed in the A-side glass substrate. As a result, in the lower A-side glass substrate, a crack extends upwardly from the scribe line Sa, and accordingly, the A-side glass substrate is broken along the scribe line Sa.
(3) Next, the bonded glass substrate 1 where the A-side glass substrate was broken is transported to a second scribing apparatus without being turned over, i.e., without exchanging the positions of the A-side glass substrate and the B-side glass substrate. In this second scribing apparatus, the B-side glass substrate of the bonded glass substrate 1 is scribed using a glass cutter wheel 2 so as to form a scribe line Sb which is parallel to the scribe line Sa as shown in FIG. 2(c). It should be herein noted that, in the case of a liquid crystal mother substrate, a plurality of liquid crystal panels are formed from the liquid crystal mother substrate, and in each liquid crystal panel, it is necessary to form terminals at a side edge portion in one glass substrate. Thus, in many cases, the scribing position of the scribe line Sa formed in the A-side glass substrate and the scribing position of the scribe line Sb formed in the B-side glass substrate are shifted from each other along a horizontal direction.
(4) Next, the bonded glass substrate 1 is turned over such that the A-side glass substrate is over the B-side glass substrate, and transported to a second breaking apparatus. In the second breaking apparatus, as shown in FIG. 2(d), the bonded glass substrate 1 is placed on a mat 4. A break bar 3 is pushed against a portion of the A-side glass substrate of the bonded glass substrate 1 which corresponds to the scribe line Sb formed in the B-side glass substrate. As a result, the lower B-side glass substrate is broken along the scribe line Sb.
By performing above steps (1) through (4), the bonded glass substrate 1 is separated into two at desired positions.
In this second separation method of a brittle material, as illustrated in steps (2) and (4), at a breaking step, the lower glass substrate to be broken has a scribe line whereas the upper glass substrate to does not have a scribe line. Thus, the upper glass substrate is not broken simultaneously with the breakage of the lower glass substrate. Therefore, occurrence of the problems which may occur in the first separation method illustrated in FIGS. 1(a) through 1(d), such as a separation face extending along an oblique direction, formation of defects, etc., can be avoided.
FIG. 3 is a side view of the glass cutter wheel 2 used in the first and second separation methods, which is seen along a direction perpendicular to the rotation axis of the glass cutter wheel 2. The glass cutter wheel 2 is formed into the shape of a disk, where φ denotes the wheel diameter and w denotes the wheel thickness, and a blade edge having a blade edge angle α is formed along the perimeter of the wheel.
The applicant of the present application further improved the glass cutter wheel 2 shown in FIG. 3 to obtain a glass cutter wheel which can form a deeper vertical crack, which is disclosed in Japanese Laid-Open Publication No. 9-188534 entitled “Glass Cutter Wheel”.
FIG. 4 is a side view of a glass cutter wheel disclosed in this publication, which is seen along the rotation axis of the glass cutter wheel.
This glass cutter wheel 5 has undulations at the edge line portion of a blade edge formed at the perimeter of a wheel. That is, U-shaped or V-shaped grooves 5b are formed at the edge line portion 5a of the blade edge. These grooves 5b are formed by cutting notches at depth h from the edge line portion 5a at pitch P. By forming these grooves 5b, protrusions j having a height h are formed at pitch P.
In FIG. 4, the grooves formed at the edge line portion are shown in a large size for the purpose of readily recognizing the grooves. However, the actual size of the grooves is a size of the micron order, which is not perceptible by a human eye.
TABLE 1 below shows specific numerical values of the wheel diameter φ, the wheel thickness w, etc. The values are shown for two examples, Type 1 and Type 2.
TABLE 1Type 1Type 2Wheel diameter φ 2.5 mm 2.0 mmWheel thickness w0.65 mm0.65 mmBlade edge angle α 125° 125°Number of protrusions j 125 110Height h of protrusions j  5 μm  10 μmPitch P  63 μm  63 μmBlade edge load 3.6 Kgf 1.8 KgfScribing speed 300 mm/sec 400 mm/sec
The glass cutter wheel having undulations at the edge line portion has a significantly improved scribing characteristic, i.e., a significantly improved ability to form a vertical crack. By performing a scribing process using this glass cutter wheel, a deep vertical crack which almost reaches the vicinity of the lower surface of a scribed glass plate can be obtained in the scribing process.
The glass cutter wheel 5 having undulations at the edge line portion has a significantly improved scribing characteristic as compared with a conventional glass cutter wheel. However, since precise undulations are formed along the entire perimeter of the edge line portion of the glass cutter wheel 5, the process and formation of the undulations in the edge line portion requires a long process time, and there are some problems in processibility.
In the case where the second separation method illustrated in FIG. 2 is performed using the glass cutter wheel 5 having undulations at the edge line portion, a scribe line Sb of a deep vertical crack is formed in the B-side glass substrate, and in some cases, the bonded glass substrate 1 is substantially separated at the time when the upper B-side glass substrate has been scribed at Step (3). Thus, when the bonded glass substrate 1 is transported using a suction pad, or the like, to the second breaking apparatus during a transition period between Step (3) and Step (4), one piece of the separated bonded glass substrate 1 may be left in the second scribing apparatus. Furthermore, during transportation of the bonded glass substrate 1, one piece of the separated bonded glass substrate 1 may fall from the suction pad. In such a case, a production line apparatus for separating the bonded glass substrate 1 may not operate in a normal manner.
The present invention was conceived to solve the above problems. An object of the present invention is to provide: a glass cutter wheel where problems in processibility, which may occur in a glass cutter wheel having undulations in the entire perimeter of the edge line portion, are solved, and a desired scribing characteristic can be obtained, i.e., a scribe line of a vertical crack having a desired depth can be formed in a glass substrate separation process; a scribing method for forming a scribe line which enables separation of a brittle material; a scribing apparatus incorporating such a cutter wheel; and a cutter wheel production apparatus for producing such a cutter wheel.